The present invention is directed to an arrangement comprising at least one integrated optical waveguide on a surface of a substrate which is composed of an electro-optical material and the arrangement has at least one electrode allocated to each waveguide, which is arranged on the surface of the substrate separated from the waveguide by an electrically insulating intermediate layer and serves the purpose of modulating or switching light conducted in the allocated waveguide with the assistance of electrical modulation or switching voltage that is applied to the electrode.
Electro-optical modulators and switches formed in a waveguide technique have been developed and employed in optical communication technology. Examples are disclosed in an article by Alferness et al "High-Speed Travelling-wave Directional Coupler Switch/Modulator for .lambda.=1.32 .mu.m", IEEE JOURNAL QUANTUM ELECTRONICS, Vol. QE-19, No. 9, September 1983, pp. 1339-1341. The preferred electro-optical material of the substrate is currently LiNbO.sub.3 because low attenuation optical waveguides can be manufactured in the substrate with a very simple technology. An example of a switch, which uses what is referred to as directional coupler principle in LiNbO.sub.3, is disclosed in an article by Auracher et al entitled "High-Speed .DELTA..beta.-Reversal Directional Coupler Modulator with Low Insertion Loss for 1.3 .mu.m in LiNbO.sub.3 ", JOURNAL OF OPTICAL COMMUNICATIONS 5 (1984), 1, pp. 7-9. In this switch, two optical waveguides are integrated at the surface of a substrate of LiNbO.sub.3. These optical waveguides extend at a slight distance next to one another in a predetermined coupling path. An electrode pair composed of two separate electrodes for applying a switching voltage is arranged in the coupling path above the waveguide over the surface of the substrate and are separated from the waveguides and the surface of the substrate by a dielectric intermediate layer. The slight distance between the two waveguides in the coupling path is dimensioned so that the crossover of light between the waveguides occurs dependent on the switching voltage.
An electrode for applying an electrical modulation voltage or switching voltage must lie in the immediate proximity of the allocated waveguide so that the radio frequency control power can be kept low. It must, therefore, be arranged on the electrically insulating intermediate layer that prevents the optical field from being attenuated by this electrode. A constant voltage for setting the operating point of the arrangement must generally be applied to one or more electrodes for applying modulation voltage or switching voltage. It, therefore, turns out that the operating point drifts away with time. The cause of this is the low conductivity of the electrically insulating intermediate layer that, however, must have a precisely defined relationship to the conductivity of the substrate of the electro-optical material. The reproducible manufacture of such an insulating intermediate layer having a specific conductivity presents extremely great technological difficulties.
If the conductivity of the intermediate layer were made significantly higher than that of the substrate, the operating point could be stabilized. However, with this increase in the conductivity, the attenuation of light in the waveguide would also be increased.